In recent years, a horizontally long television screen is becoming popular due to spread of so-called high definition and wide vision televisions. On the other hand, in consideration of Japanese housing circumstances, a television set which is narrow in width and thin in depth on the whole is desired.
A loudspeaker device (hereinafter referred to as loudspeaker) for the television set is usually mounted on both sides of a CRT display, which results in an increase in width of the TV set. Therefore, the loudspeaker having an elongated structure such as a square type, an elliptic type and the like has traditionally been used for the television set. Further, since the CRT display is lengthened horizontally, the width of the loudspeaker requires to be further narrowed down. Further, high quality in sound comparable to a high-quality screen is required to the loudspeaker. Furthermore, since a thin-screen television using a plasma display or an LCD display is becoming popular, thinning of the loudspeaker is further required.
Here, a conventional elongated (slim type) loudspeaker will be described with reference to a diagram. FIG. 21 is a diagram showing a structure of the conventional slim type loudspeaker. FIG. 21(a) is a plan view of the conventional slim type loudspeaker, FIG. 21(b) is a cross-sectional view of a longitudinal direction (c-c′) of the conventional slim type loudspeaker, and FIG. 21(c) is the cross-sectional view of a short axis direction (o-o′) thereof. The slim type loudspeaker shown in FIG. 21 comprises a magnet 101, a plate 102, a yoke 103, a frame 104, a voice coil bobbin 105, a voice coil 106, a suspension 107, a diaphragm 109, a dust cap 110, and an edge 111.
The voice coil 106 is a winding of a conductor such as copper and aluminum, and is firmly fixed to the voice coil bobbin 105 having a tubular shape. The voice coil bobbin 105 is connected to the frame 104 via the suspension 107. The voice coil bobbin 105 supports the voice coil 106 such that the voice coil bobbin 105 hangs the voice coil 106 in a magnetic gap 108 comprised of the magnet 101, the plate 102, and the yoke 103. The voice coil bobbin 105 is fixed to the diaphragm 109, having an ellipse or an approximate ellipse shape, on a side opposite to a side which the voice coil 106 is firmly fixed to. The dust cap 110, having an approximate semicircle shape cross-sectional surface, is firmly fixed on a central portion of the diaphragm 109. The edge 111 is of a ring shape, and has a semicircle shape cross-sectional surface, and an inner circumference of the edge 111 is firmly fixed to an outer circumference of the diaphragm 109. An outer circumference of the edge 111 is fixed to the frame 104.
In the case where the loudspeaker shown in FIG. 21 is driven, an electric current is applied to the voice coil 106. With a driving current applied to the voice coil and a magnetic field around the voice coil 106, the voice coil bobbin 105 performs a piston motion, the diaphragm 109 vibrates in a direction of the piston motion. As a result, a sound wave is radiated from the diaphragm 109. Note that the loudspeaker shown in FIG. 21 is described in, for example, Patent Document 1. FIG. 22 is a diagram showing a frequency characteristic with respect to a reproduced sound pressure level of the loudspeaker described in Patent Document 1. In FIG. 22, a vertical axis indicates the reproduced sound pressure level when 1 W of electric power is inputted to the loudspeaker, and a horizontal axis indicates a driving frequency. Note that a microphone to measure the reproduced sound pressure level is on a central axis of the loudspeaker and is located at a position 1 [m] away from the loudspeaker toward the front side thereof.    Patent Document 1: Japanese Laid-Open Patent Publication No. H7-298389